Treatment of bituminous sands for recovery of heavy metals therefrom

ABSTRACT

Heavy metals, especially zircon, may be recovered from bituminous sands by introducing a fluid slurry of bituminous sand into a body of water whereby a froth containing bitumen and solids floats to the top of the water and is recovered therefrom. Solids are recovered from this froth and the recovered solids are treated with sodium hydroxide and then subjected to a flotation treatment using aeration gas. During the flotation treatment, solids other than heavy metal are selectively floated and heavy metals, especially zircon, remain in the bottom of the flotation zone from which they may be recovered.

ijnited States Patent Penzes [151 3,656,938 [451 Apr. 18, 1972 [54]TREATMENT OF BITUMINOUS SANDS FOR RECOVERY OF HEAVY METALS THEREFROM[72] Inventor: Stephen Canada [73] Assignees: Canada Cities Service,Ltd., Alberta, Canada; Imperial Oil Limited; Atlantic RichiieldCorporation; Royalite Oil Company, Limited, part interest to each [22]Filed: Dec. 19, 1969 [21] App1.No.: 886,746

Penzes, Edmonton, Alberta,

[52} U.S.Cl ..75/10l,75/2, 75/121, 208/11, 23/24 Z, 23/202 [51] lnt.Cl...C22b 61/02 [58] Field ofSearch ..75/2,101,121;208/11;23/18, 23/22, 24Z, 110,140,182, 200, 202; 209/171, 167,

[56] References Cited UNITED STATES PATENTS 3,330,757 7/1967 Bichard..208/11 3,338,814 8/1967 Given et a1... ..208/11 2,696,425 12/1954Kistler ..23/140 2,082,383 6/1937 Corbett.... ....209/I66 X 2,792,9405/1957 Baarson ..209/166 Primary Examiner-L. Dewayne Rutledge AssistantExaminerG. T. Ozaki Attorney-J. Richard Geaman [5 7] ABSTRACT 4 Claims,No Drawings TREATMENT OF BITUMINOUS SANDS FOR RECOVERY OF HEAVY METALSTHEREFROM Large deposits of bituminous sand are found in variouslocalities throughout the world. The term bituminous sand is used hereinto include those materials commonly referred to as oil sand, tar sandand the like. One of the most extensive deposits of bituminous sandoccurs, for instance, in the Athabasca district of the Province ofAlberta, Canada.

Typically, the composition of these sands by weight is: from about 5% toabout 20% of oil; from about 1% to about by water; and from about 70% toabout 90% of inorganic solids. The specific gravity of the bitumenvaries from about 1.0 to about 1.05. (The specific gravity of thebitumen as well as all other values of specific gravity given herein aretaken at 60 F.) The major portion of the inorganic solids, by weight, isfine grain quartz sand having a particle size greater than about 45microns and less than 2,000 microns. The remaining inorganic solidmatter has a particle size of less than 44 microns and is referred to asfines. The fines content typically varies from about 5% to about 30% byweight of the solid inorganic content of bituminous sand. However, thecomposition of bituminous sand can vary from the above-mentioned rangesand this is not too uncommon. Also, in mining the bituminous sand, claywhich is found in layers of varying thickness in such sand areas, may beadmixed with the the inorganic solids content and particularly the finescontent of the material to be processed.

Various methods have been proposed for separation of bitumen frombituminous sand. The two best known methods are often referred to as thehot water method" and the cold water method. In the former, thebituminous sand is jetted with steam or hot water and mulled with asmall proportion of water at about 175 F., and the pulp is then droppedinto a turbulent stream of circulating water and carried through aseparation cell maintained at an elevated temperature of about 180 F. Inthe separation cell, entrained air causes the oil to rise to the top inthe form of a froth rich in bitumen which is then drawn off. Sandsettles to the bottom and may be removed therefrom.

The so called cold water method does not involve heating the bituminoussand other than whatever heating might be required to conduct theoperation at room temperature. The process involves mixing thebituminous sand with water, soda ash and an organic solvent such askerosene. The mixture is then permitted to settle at room temperature. Amixture of water and bitumen dissolved in the organic solvent rises tothe top of the settling zone and is recovered.

While the presence of zirconium and titanium in very minor quantities incoarse grains of bituminous sands has been previously recognized, thesemetals have not appeared to be present in economically recoverableconcentrations. The present invention provides a means for concentratingand recovering such metals, especially zirconium, from bituminous sands.

It has been found that when bituminous sand containing minor quantitiesof heavy metals, especially metals of Group NE of the periodic table ofelements (titanium, zirconium and hafnium), and particularly zirconium,is treated for recovery of bitumen by processes such as the abovedescribed hot and cold water methods, the heavy metals concentrate inthe bituminous froth recovered from the body of hot water to an extentsuch that recovery of the metals from the froth becomes economical. Theconcentration of metals in such froth has been found to be at least 10and frequently as much as 40 or 50 times that of the correspondingmetals in the raw bituminous sand. In the case of titanium, theconcentration in the froth is usually about times that in the raw sandwhile zirconium is usually found in the froth in about forty times theconcentrations found in the original bituminous sand. While referencesare made herein to the heavy metals themselves, it should be understoodthat such metals are frequently present in the form of oxides,silicates, etc. and when present in these forms, may be recovered assuch materials rather than as pure metal. Zirconium, for instance, istypically present primarily in bitumen, thus increasing the form ofzircon (zirconium silicate) while titanium may be present as ilmenite(iron-titanium oxide) or rutile (titanium oxide). Zircon, is usuallyenriched with minor amounts such as l to 5 weight percent (wt.%) ofhafnium. Concentrations of zirconium in raw bituminous sand arefrequently between about 0.01 and about 0.1 wt.% and the concentrationsof titanium between about 0.05 and about 0.5 wt.%. ln accordance withthe present invention, it is possible to recover at least about 30% andfrequently as much as about of these metals in froth recovered fromwater separation processes of the type described above. The solidscontent of such froth usually contains at least about 3 wt. of suchheavy metals, frequently in excess of 5 wt.%.

The present invention contemplates recovery of heavy metal, especiallyzircon, from bituminous sands by introducing a fluid slurry ofbituminous sand containing heavy metal and other solids into a body ofwater whereby a froth containing bitumen, heavy metal and other solidsrises to the top of the body of water and sand settles to the bottomthereof. Heavy metal and other solids are recovered from the froth andcontacted with an alkali metal hydroxide after which the solids arecontacted with aeration gas in a flotation zone to preferentially floatsolids other than heavy metal and form a lower layer rich in heavy metalfrom which heavy metal may then be recovered by conventional techniques.

In accordance with a preferred embodiment of the invention, bituminousfroth containing concentrations of heavy metals is produced frombituminous sand by the hot water method referred to briefly above. Inthis process, raw bituminous sand is mixed with warm water in a mixersuch as a conventional rotating cylindrical tumbler having perforationsfor the slurry to drop out and provision for rejecting oversized rocksand lumps of sand which cannot be broken down. The slurry produced inthe mixer is preferably at a temperature between about and about F. Theslurry temperature may be controlled by control of the temperature ofthe water added to the mixer or by direct addition of steam to the mixeror by other suitable means. Average residence time of bituminous sand inthe mixer is preferably between about 0.5 and about 5 minutes.Sufficient water is normally added in the mixer to form a slurrycontaining between about 20 and about 40 wt.% water. After leaving themixer the slurry is usually flooded with additional water to bring itswater content to between about 40 and about 60 wt.% and the floodedslurry is then introduced into a body of warm water maintained at atemperature between about 140 and about 200 F. If desired, aeration gasmay be added to the hot water to assist in separation of bitumen fromsand particles. Air entrained in the slurry during the mixing step aswell as any introduced into the separation zone causes bitumen to riseto the upper surface of the water to form a froth while sand is allowedto settle to the bottom. Sand tailings may be withdrawn from the bottomof the separation zone while froth containing bitumen, heavy metals andother solids is recovered from the upper portion of the separation zone.

Following recovery from the hot water separation zone, the frothcontaining bitumen, heavy metals and other solids is treated forrecovery of bitumen and metals therefrom. In a preferred embodiment ofthe invention, the froth is subjected to thermal dehydration treatmentto evaporate water therefrom and is then subjected to gravity treatmentas in a cyclone separator to obtain an overhead stream containing themajority of the bitumen and an underflow stream containing most of thesolids and substantially all of the heavy metals. if desired, theunderflow stream may be filtered to further separate liquid and solids.The solids from the underflow stream are then preferably dried as in arotary kiln.

Solids recovered from bituminous sand froth, as described above, aregenerally in the size range between about 20 and about 44 microns andcontain concentrated amounts of heavy metals. In accordance with thepresent invention, such solids are further treated with alkali metalhydroxide followed by flotation with aeration gas to further concentratethe heavy metals and especially the zirconium present in the form ofzircon. The alkali metal hydroxide is preferably in the form of anaqueous solution and, while the strength of the solution is notconsidered especially important, concentrations of between about 5 andabout 30 mol percent of the alkali metal hydroxide are commonly used.When treating the solids with the alkali metal hydroxide, enough liquidshould be used to completely wet the solids and maintain a continuousliquid phase. This may usually be accomplished with the use of at least3 volumes of liquid per volume of solids with liquid to solids ratios inthe range of about 3 to about 20 being most usual. While any alkalimetal hydroxide may be used, sodium hydroxide has been found to beespecially useful.

While the mechanism by which the process of the present inventionresults in selective flotation of solids other than heavy metal is notcompletely understood, it is believed to be due to the selective actionof the alkali metal hydroxide in stripping naturally occurringsurfactants from heavy metal solids in preference to stripping of suchsurfactants from the other solids such as silica present in the solidsrecovered from the bituminous froth. Thus, when the solids are subjectedto conventional flotation operation with aeration gas, the solids otherthan heavy metals which are still coated with naturally occurringsurfactants are floated in preference to the heavy metals which havebeen stripped clean of naturally occurring surfactants by the action ofthe alkali metal hydroxide. This operation is thus in contrast toconventional ore flotation operations in which special additives must beused either to suppress flotation effects on certain components of thesolids mixture or to enhance the flotation of some components, or both.In practicing the present invention, it is merely necessary to treat thesolids with the alkali metal hydroxide and no additives need be used inthe flotation portion of the process. Also, in conventional oreflotation processes, it is usual to preferentially float the desiredproduct solid, whereas in the present metals recovery process, theundesired solids, i.e., silica and other non-heavy metal solids, arefloated while the desired heavy metal components are concentrated in thelower portion ofthe flotation zone.

While the alkali metal hydroxide preferentially cleans the naturalsurfactants from the heavy metal solids and especially zircon, thesehydroxides do have some effect upon other solids and, accordingly, it ispreferred to limit the time of contact of the alkali metal hydroxidewith the solids so that surfactants are not substantially stripped fromsolids other than heavy metals. Also, since the temperature maintainedduring the contact effects the rate of stripping of surfactants,relatively higher temperatures are preferred in order to expedite theprocess and minimize equipment investment. Preferred conditions for thecontacting of the alkali metal hydroxide with solids recovered fromfroth in accordance with the invention include temperatures in the rangebetween about 50 and about 210 F., more usually between about 100 andabout 200 F., and a contact time between about minutes and about 2hours. Preferred contact times in the 100 to 200 F. temperature rangeare from about 15 minutes to about 1 hour.

Once heavy metal solids have been concentrated in the lower portion ofthe flotation zone, as described above, they may be recovered therefromand the heavy metal recovered in accordance with standard metal recoverytechniques.

One suitable method for recovering zirconium (with or without hafniumenrichment) and titanium from such solids involves first passing thedried solids through magnetic separation equipment to recover ilmenitetherefrom. The tailings from the magnetic separation step are thenpassed across a conventional shaking table to remove light solids,leaving zircon and rutile. These may be treated in conventionalflotation equipment with a soap collector such as sodium oleate and afrothing additive to obtain separation of zircon from rutile. It shouldbe understood that the zircon may be enriched with minor amounts ofhafnium such as up to about 5% by weight ofthe zircon.

A typical example of recovery of heavy metals from tar sands inaccordance with the present invention involves recovery of such metalsfrom bituminous sand having the following composition:

Ingredients wt.% Solids 86.12 Bitumen l0.43 Water 3.45 Hafnium EnrichedZirconium (as Zr) 0.05 (as Zircon) 0. l0 Titanium (as Ti) 0.21 (asRutile) 0.35

This tar sand is mixed with water to form a flooded slurry containing 60wt.% water and is then introduced into a hot water separation zonecontaining a body of hot water maintained at a temperature of 159 F.Froth recovered from the upper portion of the separation zone contains22.14 wt.% water, 68.50 wt.% bitumen, and 9.36 wt.% solids. Zirconium ispresent in the solids in this froth to the extent of 1.95 wt.% based onZr and 3.92 wt.% based on Zircon. Titanium is present in the solids inthe froth to the extent of 4.04 wt.% on Ti and 6.74 wt.% based onrutile. Following thermal dehydration and cycloning, the underflowsolids from the cyclone contain 70 to wt.% of the solids present in thefroth except that about of the rutile, ilmenite and hafnium enrichedzircon is present in the solids recovered from the cyclone underflowstream due to the relatively high gravity of these materials. Theunderflow solids from the cyclone are then treated with 5 volumes of 10mol percent aqueous solution of sodium hydroxide for a period ofone-half hour at a temperature of 190 F. and are subsequently contactedwith upflowing air in a flotation zone for one-half hour topreferentially float solids other than heavy metals. This results in aconcentrated layer of heavy metal solids in the bottom of the flotationzone and the solids are then removed and heavy metals recoveredtherefrom by the metal recovery techniques described above.

While the invention has been described above with respect to certainpreferred embodiments thereof, it will be understood by those skilled inthe art that various changes and modifications may be made withoutdeparting from the spirit and scope of the invention.

lclaim:

1. A process for the recovery of heavy metal compounds selected from thegroup consisting of titanium, zirconium, and hafnium metals, compounds,and combinations thereof from bituminous sand which process consistsessentially of:

mixing the bituminous sand with water at a temperature between about andabout F. to form a fluid slurry; introducing the fluid slurry ofbituminous sand containing said metals and compounds thereof into a bodyof hot water maintained at a temperature between about 140 F. and 200F., whereby a froth containing bitumen, said metals and other solidsrises to the top of said body of water and sand settles to the bottomthereof; separating said metals and other solids from said forth bythermally dehydrating the froth to remove water therefrom, andgravimetrically separating said dehydrated froth into said metals andother solids, and into a bitumen stream; mixing said separated metalsand other solids with an aqueous solution of an alkali metal hydroxideat a ratio of liquid to solids of at least 3 to 1, while maintainingsaid mixed solution and solids at a temperature in the range of betweenabout 50 and about 210 F.;

then contacting said separated mixed metals and compound thereof, andother solids in a flotation zone with an upwardly flowing aeration gasto thereby preferentially float the solids other than said metals andcompounds thereof and form a concentration in said floatation zone of alower layer rich in said metals and compounds thereof; and

and other solids is at a temperature of between 200 hour.

4. The process of claim 3 in which the metal compound is in the form ofzircon.

and about F. and for a time between about 15 minutes and about 1

2. The process of claim 1 in which the alkali metal hydroxide is sodiumhydroxide.
 3. The process of claim 2 in which mixing between the sodiumhydroxide solution and the metals and compounds thereof and other solidsis at a temperature of between 100* and about 200* F. and for a timebetween about 15 minutes and about 1 hour.
 4. The process of claim 3 inwhich the metal compound is in the form of zircon.